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Session 1: November 8, 2013

Introduction to Python for ArcGIS 10.1A hands‐on workshop offered by the Geospatial Centroid and CSU Libraries

Sarah E. Reed, PhD

Associate Conservation ScientistWildlife Conservation Society

Faculty AffiliateDepartment of Fish, Wildlife, and Conservation Biology

Introduction What is Python? Python syntax Running scripts Writing scripts Preview 2

Introduction

Introductions:

1) Name and affiliation

2) Experience using Python or other programming languages

3) How do you plan to use Python in your own GIS research or work?


Goals of workshop:

1) Introduce the Python scripting language and its application in ArcGIS 10.1;

2) Become familiar with several methods for writing, editing, and running geoprocessing scripts using Python; and

3) Apply Python scripts to automate a GIS workflow, determine the properties of a spatial dataset, and search and update attribute information in ArcGIS.


Workshop outline:

Session 1 Session 2

1) Introduction

2) What is Python?

3) Python syntax

4) Running scripts

5) Writing scripts

6) Preview

7) Review

8) Automating workflows

9) Describe object

10) Cursor object

11) Troubleshooting

12) Other topics


Demonstration 1:

SPreAD‐GIS(or why I learned Python)







a spherical spreading loss

b atmospheric absorption

c foliage and ground cover loss

d upwind and downwind loss

e terrain effects

f ambient sound conditions


cumulative noise from multiple sources


acoustic effects for species with variable auditory sensitivity



What is Python?

Applications of Python in ArcGIS:

1) Automate workflows

2) Batch process data

3) Manipulate data tables, geometry, and map docs

4) Use functions accessible only by scripts


Advantages of Python:

1) Open source

2) Cross‐platform

3) Object‐oriented

• A data structure that combines data with a set of methods for accessing and managing those data


Python editors:

Integrated Development Environment (IDE):A software application for programming and software development

Source code editor:A text editor for software code, with features specially designed to simplify and speed up writing and editing of code

Suggested Python editors:

1) IDLE

2) PythonWin (sourceforge.net)

3) PyScripter (code.google.com/p/pyscripter)

4) Others (wiki.python.org/moin/PythonEditors)



User resources:

1) Books

2) Websites

www.python.org

forums.arcgis.com

3) ArcPy site package (online)


User resources:

4) Web courses

Python for Everyone (free)

Basics of Python (for ArcGIS 10) ($32)

Using Python in ArcGIS Desktop 10 (free)

Python Scripting for Geoprocessing Workflows ($32)

Creating Python Toolboxes Using ArcGIS 10.1 (free)

Python Scripting for Map Automation in ArcGIS 10 ($32)

5) Instructor‐led courses

Introduction to Geoprocessing Scripts Using Python ($1515)


Exercise 1:

Download workshop data and verify software installation



Python structure and syntax

Python structure:

1) Programs are composed of modules

2) Modules contain statements

3) Statements contain expressions

4) Expressions create and process objects


Object:

A piece of memory, with values and associated operations; also known as variables

Types of objects:

• Numbers

• Strings

• Lists

• Files


Expression:

Processes an object: x * 2

Statement:

Performs a task, via an expression: y = x * 2

Types of statements:• Assignment: x=5

• Call: open(‘DataFile’)

• import

• print

• if/elif/else

• for, while


Module:

A library of tools; permanent file of code, composed of statements

Types of modules:

• Standard library modules: os, sys, string … (module index)

• Specialized modules or site‐packages: arcpy (site package)

a.py

b.py

c.py

Standard library modules

Your script Modules


Python syntax:

• Case sensitivity (DataFile ≠ datafile)

• Indentation

• File paths (/, \\ or r’string’)

• Quotation marks (“, ‘)

• Commenting (#)



Python structure:

1) Programs are composed of modules

2) Modules contain statements

3) Statements contain expressions

4) Expressions create and process objects


Demonstration 2:

Writing a basic script


Exercise 2:

Writing a basic script



Running a Python script in ArcGIS

The ArcPy site‐package:

1) Provides Python access to all geoprocessing tools and extensions in ArcGIS

a. All geoprocessing tools in ArcMap are provided as functions in ArcPy

b. ArcPy also includes several functions not available as tools in ArcMap

2) ArcPy has several sub‐modules with related sets of functions (e.g., spatial analyst, mapping)


Accessing the ArcPy site‐package


A Python script for ArcGIS should:



1) Include a header



1) Include a header

2) Import modules



1) Include a header

2) Import modules

3) Specify environment settings



1) Include a header

2) Import modules


4) Define variables



1) Include a header

2) Import modules


4) Define variables

5) Run geoprocessing tools


3 ways to run a Python script for ArcGIS:

1) In a Python editor (e.g., PythonWin)

2) In the Python window in ArcMap

3) As a script tool in ArcToolbox


Demonstration 3:

Three ways to run a script


Coding a workspace filepath:

1) Environment settings (arcpy.env.workspace)

2) Hard code (C:/workspace/exercise/filename.shp)

3) Create a workspace variable (“workspace” + os.sep + “filename.shp”)


Exercise 3:

Three ways to run a script


Writing a Python script for ArcGIS


3 ways to write a Python script for ArcGIS:

1) Edit an existing script

2) Export a script from ModelBuilder

3) Build a script in the Python window



General tips:1) Python is case sensitive

2) Python is sensitive to indentation

3) Filepaths use single forward slash (/), double back slash (\\), or raw string supression (r”filepath”)

4) May need to hard code filepaths (workspace + os.sep + “filename”)

5) Save scripts with the .py file extension

6) Comment out section: Alt+3 (PythonWin and IDLE)

7) Uncomment section: Alt+4 (PythonWin and IDLE)

8) Avoid schema lock: remove datasets from ArcMap

Demonstration 4:

Three ways to write a script


Exercise 4:

Three ways to write a script



Preview


Workshop outline:

Session 1 Session 2

1) Introduction

2) What is Python?

3) Python syntax

4) Running scripts

5) Writing scripts

6) Preview

7) Review

8) Automating workflows

9) Describe object

10) Cursor object

11) Troubleshooting

12) Other topics


Challenge:

Use Python!